Apparatus and method for etching glass

Abstract

A method of etching a glass sheet using a curtain coater includes supporting the sheet at its periphery and in a generally horizontal position such that it may sag under its own weight. Sagging causes the uppermost surface of the glass sheet to assume a generally concave form. Etchant solution applied to the uppermost surface flows over the glass to form a nonuniform layer on the uppermost surface. The layer has a minimum thickness at the periphery of the glass sheet. Etchant solution is applied to the glass using a curtain coater designed to handle a corrosive etchant solution. The sheet of glass is supported on a frame including a seal to prevent etchant solution from contacting a second surface of the glass.

What is claimed is: 
     
       1. Apparatus for applying an etchant solution to a surface of a glass sheet, comprising: means for applying the etchant solution to the glass sheet, said applying means including an elongated trough having a base including a slit extending lengthwise therein;   means for transporting the glass sheet at a distance beneath said applying means to receive the etchant solution, said transporting means including means for supporting the glass sheet in a generally horizontal position with a first surface thereof facing uppermost and a second surface thereof facing downward;   said supporting means configured such the glass sheet, when supported thereon, may sag under its own weight, whereby said first surface assumes a generally concave form.   
     
     
       2. The apparatus of claim 1 further including removing means for removing etchant solution from said first surface. 
     
     
       3. The apparatus of claim 1 wherein said trough has a depth of about thirty inches. 
     
     
       4. The apparatus of claim 3 wherein said trough has two ends and at least one of said ends includes a plurality of apertures disposed at different heights therein. 
     
     
       5. The apparatus of claim 4 further including means for regulating liquid flow through said slit. 
     
     
       6. The apparatus of claim 5 further including means for adjusting the distance of said applying means over the glass sheet. 
     
     
       7. The apparatus of claim 1 wherein said trough is surrounded by an enclosure. 
     
     
       8. The apparatus of claim 1 wherein said supporting means includes means for preventing said etchant solution from contacting said second surface. 
     
     
       9. The apparatus of claim 1 wherein the glass sheet has a generally rectangular periphery and said supporting means is configured to support the glass sheet at said periphery. 
     
     
       10. The apparatus of claim 9 wherein said supporting means includes a generally rectangular seal for sealing said sheet of glass about its periphery. 
     
     
       11. A method for etching a surface of a glass sheet, comprising: providing an etchant solution;   providing an elongated trough, said trough having a base including a slit extending along the length thereof, said slit having a width such that said liquid may flow therethrough at a predetermined rate;   providing a glass sheet, said glass sheet having a first surface a second surface a center portion and a periphery;   supporting said glass sheet at said periphery with said periphery in a generally horizontal plane and with said first surface uppermost, such that said first surface assumes a generally concave form;   pumping said etchant solution into said trough such that a predetermined depth of said etchant solution is maintained therein and said etchant solution flows through said slit at said predetermined rate; and   transporting said sheet of glass beneath said slit such that said etchant solution flows from said slit over said first surface to form a nonuniform layer of said etchant solution thereon, said layer having a minimum thickness at said periphery.   
     
     
       12. The apparatus of claim 11 further including removing said film of etchant solution from said glass sheet after a predetermined time. 
     
     
       13. The method of claim 11 further including providing a seal at said periphery for preventing said etchant solution from contacting said second surface. 
     
     
       14. The method of claim 11 wherein said predetermined depth is such that said etchant solution exerts a pressure of at least about 30 inches of water on said base. 
     
     
       15. The method of claim 11 wherein said etchant solution includes means for increasing the viscosity thereof. 
     
     
       16. The method of claim 15 wherein said viscosity increasing means includes sorbitol. 
     
     
       17. The method of claim 11 wherein said etchant solution includes about 48 percent sorbitol, about 4.5 percent ammonium bifluoride, about 30 percent concentrated hydrofluoric acid, and about 17.5 percent water.